Metallurgical apparatus



March 25, 1941- I c. HARDY 2,236,441

METALLURGICAL APPARATUS Original Filed Dec. 23, 1939 I I v y c fldcnsr[Freak 1077096 22 4 l a? Fine @jH dra e72 J70 flX d fl ifi gfcf OxideFrebeahr l /6 S i x s I I E L Coo/c7 [7027 Paw/er 7 INVENTOR CharlesHard BY ATTORNEYS Patented Mar. 25, 1941 PATENT OFFICE METALLURGICALAPPARATUS Charles-Hardy, -Pelham Manor, N. Y., assignor to HardyMetallurgical Company, New York, N. Y., a corporation of DelawareOriginal application December 23, 1939,.Serial No.

310,791. Divided and this application January 27, 1940, Serial No.315,963

2 Claims.

This invention is concerned with producing finely divided metal,particularly metal powders, by reduction of compounds of such metal(such, for example, as finely divided oxides) employing reducing gasesbut without substantial fusion. In its preferred aspect, the inventioncontemplates the production of iron powder directly from finely dividediron oxides by means of hot hydrogen.

' It aims to provide improved apparatus for the production of metalpowders, particularly iron,

to the end that a clean product satisfactory for use in powdermetallurgy shall be produced at low cost.

This application is a division of my copending application Serial No.310,791, filed December 23, 1939.

The manufacture of iron and steel objects by compressing and heattreating iron powders necessitates a clean starting materialsubstantially free of oxide films and non-metallicinclusions. Ironpowder of excellent quality has "been produced by electrolysis, but itis relatively expensive. Pym-metallurgical processes for the productionof iron powder andthe like are considerably cheaper but entail operatingdifficulties. Thus, there is a tendency for incomplete reduction, due tothe fact that not all portions of the oxidized starting material comeinto adequate contact with the reducing agent, with resultant inclusionof oxide or other compounds in the product. Moreover, the iron particlesas formed tend to stick together or to the walls of the receptacle. Inconsequence of these and other operating difficulties, the economiessought to be realized through the manufacture of iron powder ofsatisfactory quality by so-called sponge iron processes have not beenattained, at least to an adequate extent.

As a result of my investigations, I have devel- 40 oped improvements inapparatus for reducing finely divided metallic oxides and othercompounds, particularly iron oxide, which insure improved contactbetween reducing agent and particles to be reduced with improvement inefficiency and degree of reduction. Processes conducted in accordancewith my invention also tend to inhibit the objectionable stickingtogether of newly formed iron particlesand the like, which has beenprevalent heretofore. Moreover, my invention in its preferred embodimentpermits separation of completely reduced particles from incompletelyreduced particles during the actual reduction step. This separation issuch that particles which require more stringent treatment to bringabout reduction remain in the reduction zone for a longer period eitherby travelling therethrough at a slower. rate or over a longer path sothat their opportunity for reduction is enhanced. Thus, my inventioncontemplates, in the formation of finely divided solid metal by reducingfine particlesof a compound thereof with a hot reducing gas, theimprovement which comprises causing a bed of the particles to move alonga deck upon which the bed is supported, while passing the hot reducinggasin contact with the particles and'while imparting relative movementto the particles of the bed by shaking. In the preferred embodiment, theinvention contemplates passingthe hot reducing gas through the bed(preferably from below) and in any case transverse to the direction ofmovement of the bed while imparting a tabling movement to the bed, forexample, by shaking or vibrating the deck. In short, in the preferredaspect of my. invention the particles-to'be reduced aresubjected to atabling action while being treated with the reducing gas, with theresult that incompletely reduced (and consequently lighter) portions ofthe material tend to migrate to one portion of the table or deck whilecompletely reduced (and consequently heavier) particles tend to migrateto-another point. The completely reduced particles may be removed fromthe point to which they migrate as a finished product. The incompletelyreduced particles are removed from the other portion of the deck andare, if desired, returned to the table for further treatment.

The apparatus of my invention in preferred forms comprises in aperforated deck that forms the top of a gaschamber. The perforations inthe deck are so small that the solid particles passing thereover areprevented from passing through them. .The hot reducing gas, say,hydrogen, may be sucked through the bed into the underlying chamber butpreferably the gas is forced up- -wardly through the bed from thechamber which is maintained under a slight positive pressure.

It is preferable to preheat the material to be reduced (say, finelydivided magnetite) before sending it to the table. Likewise the hydrogenor other reducing gas should be heated to reaction temperature. In thecase of iron reduction the reaction is best conducted at temperaturesrang ing from 650 C. to 1000 C. and preferably at a temperature below800 .C. since above this temperature there is anincrease in tendency forthe sticking together of the particles.

'The used reducing gases containing the gaseous products of reduction(say, water vapor), together with excess reducing agent (say, hy-

25 satisfactory in many cases.

5 ing zone are cooled to bring about condensation of water vaporresulting from the reduction of iron oxide and the water vapor iscondensed and removed from the circuit, the residual hydrogen beingreturned to the operation after preheating.

A variety of known forms of tabling devices may be employed. Thus, aSutton-Steele pneumatic table of heat-resisting construction with aporous metal deck may be employed, the table being enclosed within afurnace chamber. The

general form of the Sutton-Steele pneumatic table is well-known and isdescribed, for example, in ,Textbook of Ore Dressing, by Truscott, 1923,page 574. Other forms of pneumatic shaking tables, such as thatillustrated on pages 938-939 of Handbook of Ore Dressing" by Taggart(1927), may also be employed.

The table may be provided with riiiies or corrugations to aid in theseparation, but tables without riiiies, such as the Sutton-Steele table,are In fact, it is possible to carry out separation and reductionsimultaneously on an inclined metal sheet which is subjected tovibration so as to impart an oscillatory movement to the overlying bed.

The deck of the concentrating table may be formed, as indicatedhereinbefore, in various ways. Thus, it may be made in the form of acorrugated metal sheet overlying the gas chamber, with rows of fineholes along the uppermost portions of the corrugations or riffles. Thedeck may also be in the form of a plain or corrugated sheet made withcontrolled porosity by compressing and heat-treating metal powders, Such"a sheet has a great number of very fine tortuous pores running throughit and is admirably adapted to serve in tion.

A variety of motions are known for bringing about concentration orseparation on shaking the operation of my inventables, and the inventionmay employ the action of pneumatic shaking tables,- such as the Sutton-Steele table, or it may employ motions heretofore employed in wettabling. A very satisfactory form of motion for a riiiled table isimparted by a pair of eccentric cams, one of which shakes the tablelengthwise and the other laterally, giving a resultant that is obliqueto the rifiies. The heavier particles of reduced metal tend to remain inthe bottom of the riflies and travel to the end of the table therein.Incompletely reduced particles are lighter and tend to ride over theriiiles passing to the side of the table. An impetus should be given tothe particles to cause them to move along the deck. This may be done byimparting a slope to the deck, or by shaking the deck in its plane witha forward stroke that is faster than the backward stroke, or by acurrent of the reducing gas which blows the particles along the deck.

In the operation of my invention, the particles on the deck are kept inalmost constant movement with respect to the deck and with respect toeach other so that new surfaces are constantly being exposedto theaction of the reducing gas.

7 At the same time, the movement between the particles tends to inhibitsticking, provided that the temperature of operation is not too high.

These and other aspects of my invention will be more thoroughlyunderstood in the light of the following detailed description taken inc0 junction with the accompanying single figure which is a flow sheet ofa preferred form of my invention employing a shaking table having aperforated corrugated deck of heat-resistant metal.

Referring now to the figure, it will be observed that there is provideda shaking table I0 enclosed within a furnace or reduction chamber H(tragmentarily shown). The shaking table has a corrugated deck H, thecorrugations of which extend parallel to each other and approximatelylengthwise of the table. The ridge of each of the series of corrugationsis perforated and has a series of small holes l3 running lenthwise ofthe ridge. The deck is disposed above and forms the top of a gas chamberId. The shaking motion is imparted to the table by a plurality ofeccentric cams. Thus, cam i5 is mounted to bump periodically against theend of the table, while a second cam 16 mounted to pump periodicallyagainst the side of the table. The table is movably' mounted onconventional supports. not shown and springs or other conventional-means (not shown) are provided for restoring the table to its originalposition after it has been bumped.

Feed to the table, for example, a magnetite sand ranging in size frommesh to 16 mesh, Tyler scale, is passed in a dry condition through apreheater ll of conventional form such, for example, as a rabbled hearthwherein it may be heated directly with a flame. The preheated feedparticles at a temperature of say 700 C. are then fed gradually andcontinuously through a chute l8 that passes through the roof of thefurnace ll, 50 that the feed is dropped on one end of the table adjacentits end bafiie IZA. Hot hydrogen gas is passed into the gas chamber I4underneath the table, passes through the periorations or pores IS in thedeck to come in contact with the particles to be reduced. The hydrogenmay be introduced into the table chamber conveniently through a flexibleconnection I9.

A bed of particles is formed upon the deck of the table and tends tomove away from the chute due to the shaking of the table brought aboutby the cams. The hydrogen gas comes in contact with the particles ofiron oxide and tends to reduce them rapidly. Particles which arecompletely reduced and hence are principally iron tend to travellongitudinally in the valleys of the corrugations and to drop off theend of the deck into a concentrate collector chute 20 and thence pass toan airtight cooler 20A. The cool finished product (iron powder) iswithdrawn item the cooler. Incompletely reduced particles tend to travelto the rear side of the table across. the corrugations. In so doing,their rate of passage on the table is substantially retarded and theyremain in the reduction zone for a longer time, coming into contact withthe hot hydrogen gas which issues from the holes in the deck. If in thetravel across the deck the particles become completely reduced they willtend to be delivered at the end of the table. Otherwise they pass offthe rear edge of the table into the point where the water condenses andis drained out of the system through a line 23. The uncondensed hydrogenfrom the condenser, together with fresh hydrogen from an exterior source24 is pumped by means of a conventional vapor pump 25 through aconventional hydrogen preheater 26 and is then returned to the gaschamber of the table through the flexible connection l9. 7

As indicated hereinbefo re, the table deck may be made as a porous metalsheet, either corru gated or plain, by powder metallurgical methods andvarious table shaking means other than the one illustrated may beemployed.

If desired, a current of gas may be blown along the table from a pipe 30that is maintained under positive pressure. This gas current, togetherwith the transverse gas current of gas forced upward through the bedtends to impart a swirling action to the lighter particles lying on thetop of the bed which aids in their reduction,

Although I have described my invention in detail with reference to thereduction of iron oxide with hydrogen, it will be apparent that oxidesand other compounds of other metals may be reduced in the process of myinvention with'various reducing gases such, for example, as carbonmonoxide.

I claim:

1. In apparatus for producing finely-divided metal particles fromfinely-divided particles of a compound of the metal. the combinationwhich comprises a chamber, a shaking table disposed in said chamber andprovided with a corrugated perforated deck adapted to support a bed ofthe ;municating with the bed therethrough, means for imparting a tablingmotion to the deck to bring about separation of'particles of diiferentspecific gravity, a supply of reducim; gas, means for preheating saidgas, means for forcing the preheated gas into the chamber underlying thedeck and through the bed, means for feeding particles of the compoundonto the deck, means for withdrawing metallic particles of high specificgravity from one portion of the deck, and means for withdrawingparticles of relatively low specific gravity from another portion of thedeck.

2. In apparatus for producing finely-divided metal particles fromfinely-divided particles of a compound of the metal, the combinationwhich comprises a chamber, a, shaking table disposed in said chamber andprovided with a deck adapted to support a bed of the particlesfmeans forirnparting a tabling motion to the deck tobring about separation of theparticles of different specific gravity, a supply of hot reducing gas,means for preheating said gas, means for passing a portion of thepreheated gas through the bed transversely to the plane of the deck,means for passing another portion of the preheated gas along the bed,means for withdrawing metallic particles of high specific gravity fromone portion of the bed, and means for withdrawing particles of.relatively low specific gravity from another portion of the bed.

CHARLES HARDY.

